PROJECT SUMMARY The opioid use disorder (OUD) crisis in the US is an epidemic of poor access to care, including medication assisted treatment (MAT) and evidence-based behavioral interventions to support MAT outcomes. Low- income, racial/ethnic minority individuals with OUD disproportionately evidence poor MAT outcomes, including less than half of individuals typically being retained in MAT at six months. Retention is one of the factors most predictive of future relapse, functioning, and mortality. Implementing evidence-based interventions to improve MAT retention that are particularly appropriate for the needs of low-income, racial/ethnic minority individuals with OUD is essential. Peer recovery coaches (PRCs), trained individuals with their own lived experience with substance use disorder, may be uniquely suited to address common barriers to MAT retention among underserved populations, including stigma, challenges navigating services, housing instability, other structural and psychosocial factors. PRC-delivered interventions are a promising strategy for improving MAT retention for low-income, minority individuals with OUD, yet there are few evidence-based interventions (EBIs) that have been evaluated for PRC delivery to promote MAT retention. Preliminary work by our team suggests that behavioral activation (BA) may be a feasible, scalable reinforcement-based approach for improving MAT retention for low-income, minority individuals with OUD by PRCs. The proposed study builds upon our team?s formative work to adapt and evaluate the effectiveness and implementation of a PRC-delivered BA intervention (Peer Activate) to support MAT retention for low-income, minority individuals initiating MAT in Baltimore City, which has one of the highest overdose-fatality rates in the US and greatest burdens of OUD among low- income, racial/ethnic minority individuals. In Phase 1, we propose to refine and finalize the PRC-delivered Peer Activate model and address barriers to implementation for Phase 2 using pre-intervention focus groups with PRCs, staff, clients, and other key stakeholders (n=24). We will establish the preliminary feasibility, acceptability and fidelity of Peer Activate in an open-label trial (n=30) and pilot Phase 2 study procedures, including collecting preliminary MAT outcomes (MAT retention and opioid abstinence at 3 months). Based upon adaptations in Phase 1, we will then conduct a randomized, Type 1 hybrid effectiveness-implementation trial to evaluate the effectiveness and implementation of Peer Activate vs. treatment as usual (TAU; n=200) on MAT retention at six months (primary), MAT adherence and opioid abstinence (urine toxicology), and depressive symptoms (secondary). Implementation outcomes will be assessed at multiple levels (patient, provider, organization), including assessments of feasibility, acceptability, fidelity, and adoption guided by Proctor?s conceptual model of implementation outcomes. Our multidisciplinary team aims to develop an evidence-based PRC-delivered treatment model that can be sustainably delivered to improve MAT retention for low-income, minority individuals with OUD.